Portable electronic devices, such as mobile cellular telephones, personal digital assistants (PDA's), digital cameras, portable audio/video devices, etc., are powered by electrical batteries, which are typically rechargeable. However, many devices use custom-sized batteries that are not removed from the electronic device for charging. For these devices, dedicated chargers are used; but as different brands and/or types of portable devices may have different charging ports, different chargers may be required. Moreover, as the physical dimensions of the portable devices are miniaturized, and/or as operation in harsh or wet environments is desired, physical contacts of the charging terminals may become increasingly difficult to implement.
Some approaches to address the above and other problems may eliminate the use of wire-based charging ports, for example, optical charging or inductive charging. In inductive charging, an inductive coupling (magnetic field interaction) may be used to provide a wireless coupling to the portable device. For example, a charging pad may include a number of electrical coils that carry an electrical current. The portable device may also contain an electrical coil. When the portable device is placed on the charging pad, an electrical current is induced in the coil of the portable device; this current is used to charge the battery.
While inductive charging may offer several advantages, disadvantages may include interference of the electromagnetic field with other electronic devices, and a lower practical limit in terms of the size of the coil and corresponding device. Also, the use of inductive coupling may limit the choice of materials for the portable device housing.
Optical charging, in which radiation in the visible or infrared (IR) region of the spectrum may be transmitted to a photovoltaic cell or other receiver in a portable device, may avoid some of these drawbacks. However, optical charging may face other challenges, for example, conversion efficiency, atmospheric absorption, and hazards presented by laser radiation.